Magnetic recording heads with monitor of recorded signal



`Iune 1, 1965 P. SMALLER 3,187,111

MAGNETIC RECORDING HEADS WITH MONITOR OF RECORDED SIGNAL F/L TEE gl, w w -Ill w S2 n s Q n g, I w

Si s( hg -AI *r 0B Q "1 Pw SAMMEQ INVENTOR.

\ wry/m ma@ June 1, 1965 P. SMALLER 3,187,111

MAGNETIC RECORDING HEDS WITH MONITOR OF RECORDED SIGNAL Filed Jan. 23, 1961 5 Sheets-Sheet 2 F/LTEE JNVENroR.

BY Agb/4mm June 1, 1965 P. SMALLER 3,187,111

MAGNETIC RECORDING HEADS WITH MONITOR 0F RECORDED SIGNAL Filed Jan. 25, 1961 3 Sheets-Sheet 5 INVENTOR.

BY )7M-)7. www

United States Patent O 3,l37,1l1 MAGNETIC RECORDlNG HEADS WITH MONIIR F RECRDED SGNAL Philip Smaller, Portola Valley, Calif., assigner to Ampen Corporation, Redwood City, Calif., a corporation of California Filed Jan. 23, 1961, Ser. No. 84,429 7 Claims. (Cl. 179-4092) This invention relates to magnetic recording and reproducing and, .in particular, to magnetic tape recording and reproducing systems wherein a signal that is being recorded may be reproduced substantially simultaneously with the recording of such signal.

In many applications of magnetic tape apparatus, such as utilized with computers and instrumentation devices, it is desirable and often necessary to deter-mine instan-taneously Whether an information signal is being correctly recorded, if at all. iIf the recording operation kis erratic, there may be a loss of extensive signal information that Awould not be available again.

In presently known recording systems, while an information signal is being recorded on a stonage medium or magnetic tape, it is generally necessary to wait for the medium or the tape to be moved away from the recording area or transducing gap before playback may be effected. However, it would be advantageous to be able to record an information signal and to reproduce such information signal substantially simultaneously with the recording.

in one type of prior art recording system, a magnetic medium may be tirst magnetized or magnetically saturated to serve as a nonlinear detector for demodulating an amplitude modulated high frequency carrier signal` One such magnetic recording system is described in U5. Patent No. 1,886,616 which is directed particularly to an audio frequency recording system. In the system described, the saturated medium demodulates the carrier Wave and records the amplitude modulating signal only. It is proposed herein to employ an amplitude modulated high frequency carrier signal in conjunction with a magnetized storage medium in a similar manner for recording and storing the amplitude modulating or information signal, and in addition concurrently reproducing the recorded information signal only.

An object of this invention is to provide a recording system lwherein a recorded signal may be instantaneously reproduced during recording.

`Another object of this invention is to provide a magnetic recording and reproducing device wherein a relatively low frequency `signal may be recorded and simultaneously reproduced.

According to this invention, a magnetic recording and reproducing system comprises a means .for applying an amplitude modulated high frequency carrier signal to a magnetic transducing device, a magnetic storage medium for traversing said device to demodulate and record the amplitude modulating signal only, and an output circuit means coupled to the device for simultaneous readout of the recorded signal. Additional means, such as a low pass iilter, may be provided to attenuate or cancel any spurious component of the high frequency carrier signal in the output circuit so that only the information or amplitude modulating signal is effectively reproduced.

ln a particular embodiment of the invention, the trans- -ducing device may comprise a plurali-ty of magnetic cores or parts coupled in such manner that the recorded amplitude modulating signal is reinforced for processing -by the output circuit, whereas the high frequency carrier signal is cancelled or bucked out and therefore does not appear in the .output or utilization circuit. Therefore, only the recorded information signal is effectively reproduced in ythe output circuit for verification or a parity check.

The invention will be described in greater detail with reference to the accompanying drawing, in which:

FIGURE 1 is a schematic and block diagram showing a magnetic recording and reproducing system, in accordance with the invention; and

FIGURE 2 and 3 show falter-native embodiments of the .same invention.

In FIGURE l, a magnetic transducer lll comprises a magnetic core l2, which m-ay be formed from Permal-loy or Mumetal, or a ferrite core having Alfenol pole tips, for example. A sign-al generator 14 provides ra high frequency carrier Wave Which is amplitude modulated in a modulator lo by relatively low frequency information signals, such as an audio frequency signal or pulse signal information, derived from a signal source lil. The amplitude modulated high frequency carrier signal is directed to an input coil Ztl coupled to the core l2 thereby causing linx variations in a nonmagnetic transducing ga-p 22. formed in the core, in a well-known manner. To record the information signal, a magnetic medium or tape 24, which has been previously magnetized to serve as a nonlinear detector, traverses the gap Z2 and demodulates the high frequency carrier Wave.

With the information signal only recorded on the magnetic tape 24, variations in flux are produced in the transducing gap Z2 in accordance with amplitude variations lof such recorded signal. The flux variations develop current Variations in the core l2, which may be sensed and utilized in an output circuit. For this purpose, and output coil 2o is coupled to the core 12 for channelin such varying current to a utilization circuit 23, Wherein the electr-ical current variations may 'be utilized for readout of the recorded amplitude modulation signa-l. However, since the output coil 2o may also receive a portion of the high frequency carrier signal from the input circuit directly through the core l2, a 10W pass filter Sil is coupled between the output coil 26 4and the utilization circuit 2S to cancel or attenuate the undesirable high frequency carrier signal thereby preventing the appearance of any high frequency carrier component in the utilization circuit 23. In this manner, a signal being recorded may be effectively reproduced concurrently with the recording.

in FIGURE 2, another embodiment of the invention includes a magnetic transducing assembly comprising a magnetic core 33 .in substantially rectangular form, and an intersecting leg dii dividing the core Sil into two :branche-s 42 and 4d. The lfirst branch d2 serves as a rec- ;or-d section, 1and has a recording gap lo adjacent to the leg dit coupled to an input signal providing means for recording an information signal on a magnetic medium or tape d8. The second branch ed serves as la reproducing section and has a reproducing gap Sil closely spaced from the recording gap 46 by the intersecting leg 40.

As in the embodiment of FlGUR-E l, an input signal, which is `an amplitude modulated hgh frequency carrier signal derived `from a carrier signal generator 14 and information signal source ld and modulated in a modulator le, is simultaneously channeled to interconnected coils 58 and oil coupled respectively to a leg 62 of the reproduce Ibranch da and to the intersecting leg d@ common to both branches 42 and 44. The amplitude modulated carrier signal appears in the record branch 42 and develops a flux field at the record gap d6 which varies in accordance with the variations in input signal. yCoils 53 and 60 are interconnected in such manner that the direct-ion of the iiux fields =at any instant during the recording process aid to reinforce the record signal at the record gap 46, while the amplitude of the modulated carrier signal is eiiectively minimized, at the gap Sil as .a result of the opposing flux iields, as `shown for the purpose of example lby the directional `arrows '6l in FIGURE 2.

Alayer of the tape.

yspaced discrete gaps. l

is not limited only to the embodiments shown herein, butr encompasses generally such structures'that process a highl The magnetic tape d, which may be magnetically saturated to act as a nonlinear detector, traverses the record gap 46 and demodulates the carrier signal so that the amplitude modulating signal is stored on the magnetic Therefore, only the recorded amplitude modulating signal on the tape 483s sensed at the reproduce gap 50 and passed to an output processing means by a coil 64 that is coupled to an arm 66 of the s reproduce branch 44. The output signal from the coil 64 is then directed to a low pass filter 63 and to a utilization circuit 7u in a manner similar to'that described with reference to FIGURE 1. In this Way, it is possible to check the information signal recorded on a magnetic tape substantially simultaneously with the recording thereof.

In FIGURE 3, another embodiment of the yinvention includes a magnetic transducing assembly having two spaced magnetic cores 74 and 76, both substantially rectangular in form'. The core 7d serves as a record-reproduce transducer and has a transducing gap 78. The core 76, which acts as a bucking core, iscoupled to the transducing core 74 by a coil Si) that receives the input signal or the amplitude modulated high frequency carrier signal. The core 76 is preferably magnetically shielded from the core 74 by proper spacing, or in any other known manner, to prevent crosstalk.v

The amplitude modulated high frequency carrier sigt nal, such as utilized in the embodiments of FIGURES 1 and 2, is supplied simultaneously to the cores 74 and 76 l from a carrier signal generator 14 and information signal Y ages induced in each of the coils 86, $8 bythe carrierV signal applied tocoil 8) are in opposition or in antiphase at any given instant. Thus, the modulated carrier input 'signal' is practically negated at the output of the coils 86 and 88.

For additional attenuation of the undesirable carrier signal in the output circuit, a loW pass filter 90 may be coupled between theV output of the coils 86 and 8S andV an output or utilization circuit 92 to prevent any portion of the high frequency carrier signal that may pass from the outputof coils 86 and 88 from appearing in the l utilization circuit 92. l

In operation, as a magnetic tape 84 traverses the transy f ducing gap 78, the tape 34, which hasbeen previously magnetized, demodulates the amplitude modulating signal only on the tape. The recorded signal then appears at Y the transducing core 74 in the formof magnetic flux that causes asignal current corresponding to its amplitude to v'be developed in the output coil 86. In this manner, the

amplitude modulating information signal may be processedwithout any spurious high frequency carrier components by the utilization circuit 92 Vfor instantaneous readout.

There has been described herein a novel magnetic transducing assembly wherein recording and playbackY are provided substantially simultaneouslyso that verification of the recorded signal may be achieved during the recording process. It is noted that the illustrated systems may employ either a single transducing gap or very closely lt is understood that the invention frequency carrier signal amplitude modulated by a relatively low'frequency signal, Which'is demodulated and recorded by a magnetized storage medium, and then reproduced from the medium practically simultaneously Vwith the recording thereof by means rejecting the high frequency carrier signal.

What is claimed is: 1. A Ymethod for simultaneously recording and reprosignal to a transducing device for recording said amplitude modulating information signal only; demodulating and recording such information signal on a magnetic medium which has been magnetized to act as a'nonlin'ear detector;

sensing the recorded signal for application to a utilization circuit; and attenuating the high frequency carrier signal to'prevent its appearance in the utilization circuit.

2. A magnetic recording and reproducing system comprising: a magnetic transducing device having at least one nonmagnetic gap; an input signal means vcoupled to said device for providing a high frequency carrier signal modulated by a relatively low frequency information signal; a movable magnetic storage medium for demodulating and recording said information signal at said gap; and an output signal processing means, including a low pass lter coupled torsaidtransducing device for reproducing only said information signal simultaneouslywith the recording thereof. f

.3. An apparatus for recording audio frequency signal information onto a movable magentic medium and for instantaneous playback of saidrsignal information coming said recorded low frequency signal While suppressing,V

said carrier signal; andV a utilization circuit for processing said filtered information signal practically ksimultaneously With the recording of said information signal.

c 4. A magnetic transducer assembly for recording an amplitude modulating information signal, on Va movable magnetized storage medium comprising: a magnetic core having an intersecting leg forming a recording branch and a playback-branch, each branch having a nonmagnetic gap closely spaced adjacent to saidintersecting leg; a first coil coupled to said intersecting leg and said recording branch; a second coil coupled to a leg of said playbacl-i branch, said coilsbeing interconnected so that the magnetic iiux in said branchesare in opposition at any given instant; means for applying an amplitude modulated high frequency carrier signal to said coils so that said information signal only may be recorded by said storagemedium said information signal comprising: a first magnetic core having a transducing gap; a second magnetic corehavingsubstantially equivalent magnetic and electrical characteristics to said first core; an input coil coupled to said rst and second magnetic cores for providing an amplitude modulated high frequency carrier signal to said cores; input means for generating a'high frequency carrier signal and for modulating said carrier signal With said in- Y formation signal coupled to said input coil; a magnetically saturated magnetic tape for traversing said transducing gap to record said information signal only; a first output coil coupled-to said first magnetic core for passing the recorded signal to an output circuit; a second output coil coupled tofsaid'second magnetic core andconnected to said first output coil for cancellation of any'component of the carrier signal; a low pass filter means coupled to the output of said Vfirst -andsecond output coils for attenuating any high frequency signal that may appear in the output circ-uit; and a utilization circuit coupled to the output of said filter means for reproducing the recorded information signal simultaneously with the recording thereof.

6. A method for simultaneously recording and reproducing an information signal comprising the steps of: applying a modulated high frequency carrier signal to a magnetic transducing device for recording said modulating information signal only, said device including a single active transducing gap; recording such information signal on a magnetic medium Which has been previously magnetized to act as a nonlinear detector; and utilizing the recorded signal for instantaneous playback via said single gap.

7. In a recording system, a recording medium transducer means for recording and reproducing having a single active transducing gap and in transducing relationship with said recording medium, means for applying a signal to be recorded to said transducer means, said means operatively coupled to said transducer; second means for simultaneously detecting said signal actually recorded by said transducer via said single gap, said record means operatively coupled to said transducer means.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Stewart, W. Earl: Magnetic Recording Techniques, page 30, 1958, McGraw-Hill Book Company, Inc.

IRVING L. SRAGOW, Primary Examiner.

NEWTON N. LOVEWELL, BERNARD KONICK,

Examiners. 

2. A MAGNETIC RECORDING AND REPRODUCING SYSTEM COMPRISING: A MAGNETIC TRANSDUCING DEVICE HAVING AT LEAST ONE NONMAGNETIC GAP; AN INPUT SIGNAL MEANS COUPLED TO SAID DEVICE FOR PROVIDING A HIGH FREQUENCY CARRIER SIGNAL MODULATED BY A RELATIVELY LOW FREQUENCY INFORMATION SIGNAL; A MOVABLE MAGNETIC STORAGE MEDIUM FOR DEMODULATING AND RECORDING SAID INFORMATION SIGNAL AT SAID GAP; AND AN OUTPUT SIGNAL PROCESSING MEANS, INCLUDING A LOW PASS FILTER COUPLED TO SAID TRANSDUCING DEVICE FOR REPRODUCING ONLY SAID INFORMATION SIGNAL SIMULTANEOUSLY WITH THE RECORDING THEREOF. 